The invention relates to medical devices for treating cardiac conditions, and more particularly, to medical devices using an electrocardiogram.
An electrocardiogram (ECG) is a recording of the electrical activity of the heart conducted through the body of a patient. The ECG records the difference in potential between two or more electrodes placed upon the body of the patient. In some circumstances, several electrodes are placed on the patient. In other circumstances, such as an emergency situation in which sudden cardiac arrest is suspected, fewer electrodes may be used.
An automated external defibrillator (AED) is an example of a device that may employ two electrodes to record an ECG. An operator such as an emergency medical technician attaches one defibrillation electrode to the upper right side of the chest of a patient who is suspected of experiencing cardiac distress. The operator attaches another defibrillation electrode to the lower left side of the chest. The AED generally measures the patient""s ECG automatically, using the defibrillation electrodes as sensors. The AED also assesses whether a defibrillation shock is indicated based upon the ECG, and charges a storage element in preparation for giving the shock. When a shock is indicated, the AED may cue the operator to administer the shock, or the AED may administer the shock automatically. The patient receives the shock through the same electrodes.
The treatment provided by the AED to the patient depends upon the ECG signal. One factor that may influence the clarity of the signal is the quality of the connection of the electrodes to the patient. In the case of a patient with a hairy chest, for example, an electrode placed on the chest may lose contact with the patient""s skin, resulting in a poor electrical connection.
In addition, the electrical activity embodied in the ECG signal may be influenced by factors such as a pacemaker. A patient having an apparently abnormal heart rhythm may actually be having the heart rhythm controlled by a pacemaker. In such a case, the AED should recognize the presence of pacing, and may adjust its analysis of the ECG signal.
The invention is directed to techniques for identifying and/or monitoring signals of interest detected by electrodes on the body of a patient. One of the signals is the patient""s electrocardiogram. Other signals include a signal that identifies the presence and timing of signals from a pacemaker in the body, and a signal that reflects the quality of the electrical connection of the electrode to the body. These signals are received superimposed upon one another, and are separated with digital filters.
In an exemplary implementation, the electrical signal from the body is passed through an anti-aliasing filter and is then converted to a digital signal. A digital signal processor digitally filters the digital signal to monitor the ECG signal, identify pacemaker signals and assess the quality of the electrical connection. In addition to generating these signals with digital filtering, the digital signal processor may analyze the signals. In addition, the digital signal processor may control a subsystem such as defibrillation circuitry, based upon the analysis.
In one embodiment, the invention presents a device comprising a first digital filter that receives a digital signal representative of a signal from a body and generates a pacemaker signal as a function of pacing pulses supplied by a pacemaker and a second digital filter that receives the digital signal and generates an electrocardiogram signal. The device may further include a third digital filter that receives the digital signal and generates a signal indicative of the quality of the electrical connection of an electrode to the body. This embodiment may be employed in many environments, including an electrocardiogram system in a hospital or an AED out in the field.
In another embodiment, the invention presents a method comprising digitally filtering an electrical signal representative of a signal from a body to generate a pacemaker signal as a function of pacing pulses supplied by a pacemaker and digitally filtering the electrical signal to generate an electrocardiogram signal. The method may include commencing a defibrillation sequence, depending upon the analysis.
In a further embodiment, the invention presents a device that includes an analog-to-digital converter and a processor. The processor performs the digital filtering operations. The processor may further perform the analysis of the signals obtained by digital filtering.
Digital filtering brings about many benefits. For example, digital filters are smaller than conventional analog filters, thus saving space and weight. Digital filters are easily programmed and easily adjusted. Digital filters are generally more reliable than their analog counterparts. Digital filters may also be inexpensive.
The above summary of the invention is not intended to describe every embodiment of the invention. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.